1. Field of the Invention
The present invention relates to an apparatus for treating emissions of manufacturing plants having particular characteristics and structure. The invention is particularly well adapted for use in steel-plants with electric arc furnaces. For illustrative purposes the invention is described below with respect to its use in steel-plants, however, this invention is not intended to be limited solely to the use with steel-plants.
2. Discussion of the Background
A known example of an apparatus for treating the emissions of a steel-plants is described below with reference to the schematic diagram depicted in FIG. 1. A conventional example of a steel-plant emission treatment system includes an emission stream 2 that exist a furnace (not depicted) and accesses a treatment apparatus 1 through an elliptical duct 3. At the top of the duct 3 there is a movable flange 4 which adjusts the inflow of air (indicated by the arrow 10) into the duct 3. The injection of the air stream 10 produces a first cooling of the stream 2. Downstream of the movable flange 4, the duct 3 widens in order to take into account the greater volume of the conveyed fluid. The duct 3 conveys the mixture of emissions and air (designated by the arrow 5) toward a decantation chamber 6. During travel along the duct 3, the mixture 5 undergoes further cooling by convective exchange with the walls of the duct 3. The decantation chamber 6 separates the metallic particles (cooled molten drops) entrained by the emissions in the duct 3. In general, the walls of the decantation chamber are made of refractory cement to ensure adequate thermal insulation.
From the decantation chamber 6, the mixture 5 accesses a vertical duct 7 and then a divergent outlet duct 8. At the outlet of the decantation chamber, the air and gas mixture 5 is subjected to an injection of nebulized water by means of an array of nozzles 9. This injection of water, together with the path along the vertical duct 7, cools the mixture 5 before it is fed to the subsequent filtration stage (not depicted) and then into the atmosphere. FIG. 2 is a side view of the vertical duct 7. Duct 7 has a rectangular cross-section in its upper part, whereas its lower part has a hopper-like tapering region 11 on two sides.
Conventional apparatuses for treating the emissions of steel-plants suffer from a problem where the cooling of the emissions at the outlet is insufficient due to the non-uniform flow of the emissions. This problem is even more severe if the size of the steel-plants need to be compact.
The path of the emissions through a conventional emission treatment apparatus is depicted schematically in FIG. 3. The inlet emissions 2 are mixed with an air stream 10. The gas mixture 5 reaches the decantation chamber, where vortical structures (represented schematically by the arrows 15 and 16) are generated. Part of the mixture 5 directly accesses the vertical duct 7, while the remainder continues to recirculate in the decantation chamber due to the vortices generated inside the decantation chamber. Due to the presence of the vortical structures 15 and 16, vortical structures (represented schematically by arrows 18 and 19) are generated proximate to the array of injection nozzles 9. The presence of the vortices produces severe non-uniformity in the field of motion of the mixture in the region where the nozzles are installed. This non-uniformity causes malfunctions of the nozzles and therefore inadequate cooling of the mixture that accesses the outlet duct 8. The increase in the temperature of the gases leaving the duct 8 can damage the filtration stages (not depicted) located downstream, thereby reducing their reliability and their residual life.
Other conventional alternative embodiments solve the problem of the uniformity of the stream of emissions inside the emission treatment apparatus by increasing the dimensions of the inlet and outlet ducts. However, this solution is expensive and would make the plant scarcely competitive from the economic point of view. Moreover, these solutions, due to their considerable dimensions, can seldom be adopted because they considerably increase the area occupied by the steel-plants, with a considerable increase in its operating costs.